The invention relates to stereoscopic imaging methods in radiology. It relates in particular to the displaying of an endovascular prosthesis, generally called a stent, in a vessel.
Stents are prostheses which are widely used to enhance or increase the diameter of a vessel or an artery. These stents are generally cylindrical elements having a periodic lattice structure which allows them to be deployed radially. During a surgical procedure comprising implanting a stent in a vessel, the operator must ensure that the stent has been positioned and deployed satisfactorily. This verification is essential in order to avoid any subsequent risk of new stenosis, that is, a new retraction of the vessel walls. For this purpose, the operator performs an X-ray angiography to display the patient""s vessel or artery into which the stent has been implanted. The disadvantage of this technique is that the images are obtained by projection, which therefore gives only a two-dimensional view of the stent. The operator may display the vessel using intravascular ultrasound (IVUS) techniques to obtain, for example, cross-sectional images along the axis of the stent. However, these techniques require the insertion into the vessel of an ultrasound probe carried at the end of a specific catheter, the catheter being connected to an IVUS imaging apparatus.
Furthermore, stents are particularly difficult to display on X-ray angiographic images because of their small thickness. This low opacity is generally due to the low density of the material of which they are made and to their geometrical configuration in the form of a lattice, which has a high proportion of empty spaces.
An embodiment of the invention provides a method for displaying an element having a periodic structure, such as a stent, images of which are acquired by means of a radiography machine of the type comprising means for providing a radiation source, such as an X-ray source and means for detection placed opposite the source, wherein the images obtained are displayed with an overall magnification of:                     f        S                    f                  C          ⁢                      xe2x80x83                    ⁢          S          ⁢                      xe2x80x83                    ⁢          F                      xc3x97    E    ⁢          xe2x80x83        ⁢    S    ⁢          xe2x80x83        ⁢    D    xc3x97          π      180        ,
where fS is the fundamental frequency, being the inverse of the spatial period of the stent in pairs of lines per millimeter;
where fCSF is a spatial frequency corresponding to the contrast sensitivity maximum for the human eye in cycles per degree; and
where ESD is the expected distance in millimeters between means for displaying images and an observer viewing these images.
An embodiment of the invention is a system for displaying an element having a periodic structure, such as a stent, comprising means for image acquisition in a radiography machine, the machine comprising means for providing a source of radiation and means for detection placed opposite the source, means for display, and means for processing for implementing the method.